At our home in the San Francisco bay area, we're building a small outbuilding that will have an unheated garage as well as a room whose interior dimensions will be approximately 18'x9' with a cathedral ceiling whose peak is about 10'. (162 square feet.) It will be new construction (R13 insulation in the walls and floor, R30 in the roof; double-paned windows). The room will be primarily used as a gym, and one day possibly as a doghouse (for one dog). Given that use, and the fact that we'll probably only be in there a few times a week, humidity/ventilation is a bit of a concern (we really don't want it to become musty/damp/mildewy).
As the room is so tiny, we don't want the solution we pick to take up any floor space in the room. We had thought that maybe the HVAC system could be mounted in the rafters/roof trusses of the garage and go through the wall into the gym.
From the information at http://www.acdirect.com/systemsize.php, it looks like we need a heating system that can do approximately 5,700 BTU/hour.
Energy efficiency is also a big concern--we have to get this approved by the "green building consultant" with our city.
We did find an air to air heat exchanger that also includes a small heat pump (the Nilan VPL-15, listed at http://www.nilan.ca/indexen.htm and http://www.nilan.ca/hvac-book-pdf/nilan-vpl15-vpl25-flyer.pdf). It looks ideal for our needs, but it's rather expensive, so we're hoping there might be something much more cost-effective.
Any suggestions would be most appreciated.